The Rams were clearly not happy with Watkins so I would go with their behind the scenes look at him.
Buffalo gave him up.
Rams picked him up. Goff clearly didn't trust him. McVay clearly didn't trust him. Rams made little effort in retaining him.
Rams pay up to get another receiver.

That is the Sammy Watkins story thus far. There is something that we don't know. It's not just the lack of stats. It's not just his perceived lack of effort in fighting for balls. It's the story that we can't read too. There is too many question marks and only one variable. It's Sammy. Whether he still has planting issues with his foot (past injuries), doesn't put in the work during an individual play, game or in the film room or maybe he just isn't as good as we want him to be there is something amiss.